Buckskin changing color
 

Normal yellow with dorsal stripe and 4 black stockings to the knee. That's in summer. In winter he turns sooty but not always the same way. One winter his black stockings climbed right up to his belly and the stifle on the rear with sooty haze on his shoulders. Another time it was his cheeks and neck that became sooty but his stockings didn't grow. I call it sooty as that's how it looks from a distance but up close it a shiney bronze, like the shine of Akhal Teke's. Any one else have a buckskin that does this? I suppose someone will tell me it's a dun.

I haven't had Abby get dark, like you describe, but she looks dingy and kind of brownish. She looks shiny still because she has like metallic gold hairs mixed in (like people with blonde hair).

Do you have any pictures?

Horses often get darker colored in winter. It can vary from year to year depending on how much of a winter coat they grow.

I had one that went from brown to almost black, especially on the face and legs and shoulders.

My buckskin's changing colour with his winter coat... only he's getting white :O

My mare every winter turned sooty. In the spring she was regular. In the summer she was metallic. In the fall she was almost roany. I think it's normal :) Also if she has a true dorsal stripe she IS dun. My mare was also dun but since she had the buckskin coloring I always called her that instead.

No, buckskins can have a dorsal stripe. It's just called countershading.

And a horse can be a "dunskin", so buckskin with dun markings, which was probably the case of your mare, jyuukai, or she was just a buckskin with countershading.

Abby is shedding out a decent amount finally, and she has random sootiness on her. Particularly, her jaw, withers, shoulders, and hips. It looks like she rolled around in dirt, but it's dark hairs. I imagine she'll continue to shed out and then lighten up to normal.

That's why I said true dorsal stripe. Countershading and a dorsal stripe aren't the same thing.
My mare was definitely a dun with buckskin colorings. She also had the barring on her legs to prove her dun gene. I hate the term dunskin though, along with dunalino. Ugh, I don't know why, those two things just bother me lol.

Instead of dunskin, then she'd be a buckskin dun. The dun gene can affect any colour.

A dorsal stripe and countershading can look very similar, but a horse only has the dun gene if it has other dun factors.